1. Field of the Invention
This invention is directed in general toward a device for backlighting an indicating instrument and more specifically to a reflector that evenly and efficiently distributes light to modules in a vehicle instrument cluster.
2. Discussion of Related Art
Traditionally, analog instrument clusters on vehicle instrument panels have been illuminated by an arrangement of light guides, reflectors and light bulbs. For example, U.S. Pat. No. 5,556,187 illustrates a speedometer dial lit by multiple bulbs. One reflector guides the light from the bulbs to a pointer mounted on the dial. Another reflector concentrates light from the bulbs onto the first reflector. This requires a high part count and a large space requirement that reduces packaging efficiency. The use of bulbs shortens the life of instrument clusters. In those clusters that use light guides to transmit the light from bulbs to a dial face, the dial face is often unevenly lit with some sections being brighter or dimmer than other sections. Those sections furthest away from the bulbs are dimmer. A dial or indicating instrument is typically made from a clear or transparent piece of plastic. Portions of the dial other than the numbers and tick marks are then screenprinted with colors such as black or white. To provide uniform lighting across the dial, those sections that would ultimately be brighter when the dial is backlit are given additional screenprinted spots or layers. These are called compensation passes and add considerable cost to the production of the indicating instrument.
Light emitting diodes expend considerably less power than light bulbs, but more are needed to provide adequate illumination. Devices have been developed in other environments to reduce the need for large clusters of light emitting diodes. U.S. Pat. No. 5,896,093, for instance, sets forth a light assembly for a traffic sign. A fluted lens is used to magnify and focus the light from a relatively small set of light emitting diodes, increasing the intensity of the light and the distance at which the sign can be viewed.
Reflectors with multiple fluted sections are known in the art. For example, U.S. Pat. No. 3,705,303 discloses a reflector for fitting over a lamp. The reflector has an upper fluted conical section and a lower fluted skirt portion that flares outward. It is used in combination with a refractor to spread light simultaneously over large floor and ceiling areas. Reflectors with variously shaped parts have also been used for backlighting displays. U.S. Pat. No. 5,567,042 describes a backlight unit for a liquid crystal display, the unit including a reflector. The reflector has a reflective surface having a series of differently shaped sections. Some of the sections are parabolic to collimate fluorescent light so it is directed toward the display.
Accordingly, it is an object of this invention to provide a reflector that evenly distributes light across a viewing surface of an indicating instrument.
Another object of the invention is to enable a small number of light emitting diodes to deliver outstanding backlighting for an indicating instrument.
A further object of the invention is to furnish an indicating instrument that has few parts, is easily assembled, and is inexpensively and efficiently backlit.
In carrying out this invention in the illustrative embodiment thereof, a reflector has first and second sets of flutes, and apertures for receiving two light emitting diodes. The flutes are located in a semi-bowl-shaped chamber or compartment behind an indicating instrument. The flutes of the first set are parabolic and centrally located in the compartment. The flutes of the second set extend radially outward from the first set. The apertures are located in a predetermined position within the chamber adjacent the radial flutes. An indicating instrument with a backlightable scale is assembled on a first side of the reflector over the chamber. A printed circuit board having two light emitting diodes is assembled on a second, opposite side of the reflector such that the two light emitting diodes protrude through the apertures into the chamber. The parabolic nature of the first set of flutes spreads the light radially outward, in an even fashion. The radial flutes diffuse the light and prevent bright or hot spots from forming under the indicating instrument. The undersurface of the indicating instrument has a reflective chrome coating that prevents absorption of the light and helps scatter it evenly across the indicating instrument.
The reflector provides even backlighting without dial compensation. It also furnishes an intensity of greater than ten candelas per meter squared with the use of only two light emitting diodes.